The plan involved using the now-dormant Hell of Blazing Fires as a super-high temperature furnace in an attempt to tame a power that it is said the outside world won't attain for hundreds of years: nuclear fusion energy.

その第一段階として、優秀な地獄鴉の選定。
太陽の化身、八咫烏の付与。
灼熱地獄跡の再燃。
そして鴉の飼い慣らしである。

The first step was to find an exemplary hell raven.
Then, to bestow upon it the personification of the sun, Yatagarasu.
Then, to rekindle the flames of the Hell of Blazing Fires.
Then, to tame the crow.

Unlike fission energy, fusion reactions are less likely to go out of control. In addition, it doesn't create such lethal waste. So, because it is very safe and produces massive amounts of energy, it is an almost dream-like energy production method.

神奈子は神社の営業の一環として行動したようである。

Kanako seems to treat this as just one part of the shrine's operations.

特に危険は感じられなかったので、真相が判った後も地上の妖怪
は計画を潰すような事はしなかった。

Because they didn't feel the plan was dangerous, the above-ground youkai did nothing to stop it even once they found out the truth.

ただ、地底に行かされた霊夢達は
『そういう事はみんなに言ってからやれ』
とカンカンだったそうな。

However, Reimu, who was made to go underground,
confronted them and said angrily,
"Next time, tell everyone about it before you start!"